Project Summary The development of end stage renal disease (ESRD) carries devastating implications for patients, including increased morbidity and mortality, lost productivity, and impaired quality of life. The burden of this disease disproportionately falls on the country's most disadvantaged communities. In preliminary work for this grant, we found that 25% of patients aged 19-64 are uninsured at the time of initiating dialysis. This poses a barrier to receiving nephrology care prior to dialysis and initiating dialysis with an arteriovenous fistula rather than a high-risk temporary catheter. Failure to access these pre-dialysis services strongly predicts worse outcomes after dialysis including hospitalizations and death. Further, kidney failure due to diabetes and hypertension (the two most common causes of ESRD) can be prevented or delayed with appropriate blood pressure and glucose control. However, the uninsured have limited ability to finance health services and often forego effective preventive and chronic disease care. Taken together, these findings suggest that expanding health insurance coverage may be a powerful strategy to address disparities in the outcomes with and incidence of kidney failure. But there is limited research to confirm or refute this assertion. Filling this gap in knowledge is critical, since the Affordable Care Act (ACA) provides states with the option to expand Medicaid coverage to residents with income less than 138% of the Federal Poverty Level. Rigorous empirical evidence about the consequences of expansion, particularly for high-cost, high-need populations, may inform these decisions but are currently unavailable. Using clinical data from all incident patients with ESRD in the United States from 2009-2018, our specific aims are: 1. Assess the effects of Medicaid expansion on pre-dialysis care for low-income incident populations; 2. Assess the impact of Medicaid expansion on post-dialysis outcomes; and 3. Evaluate early effects of Medicaid expansion on the incidence of ESRD. Our central hypotheses are that Medicaid expansion improved access to recommended pre-dialysis care; reduced hospitalizations and mortality following dialysis; and lowered the incidence of kidney failure, particularly among minority populations and those living in low- income neighborhoods. The proposal is innovative, as we leverage the variation in state Medicaid expansion decisions to test the causal effect of increased Medicaid coverage for a high-risk population. Further, by geocoding patient addresses we will track Census-Tract level outcomes, test alternative approaches for small area estimation, and assess geographic discontinuities across state borders. This project will provide rigorous evidence about the public health and health equity implications of a key feature of the ACA, perhaps the most consequential health care legislation since the passage of Medicare and Medicaid in 1965.